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<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>
    <p>属性没有值</p>
    <input type="text" value="John Doe" disabled>
    <p>属性值没有引号</p>
    <input type="text" value=John Doe>
    <p>属性值双引号</p>
    <input type="text" value="John Doe">
    <p>属性值单引号</p>
    <input type="text" value='John Doe'>
</body>

</html>